In an information recording medium, such as an optical disc, like a CD-ROM (Compact Disc-Read Only Memory), a CD-R (Compact Disc-Recordable), and a DVD-ROM etc., for example, there has been also developed an optical disc of a multilayer type, dual layer type or multiple layer type in which a plurality of recording layers are laminated or stacked on the same substrate. More specifically, a dual-layer type optical disc has a first recording layer (referred to as a “L0 layer” in this application, as occasion demands) as a first layer, which is located on the nearest side (i.e. on the closest side to an optical pickup), viewed from the irradiation side of laser light, in recording by an information recording apparatus. Moreover, it has a semi-transparent reflective film located on the rear side of the first recording layer (i.e. on the farther side from the optical pickup). The dual-layer type optical disc has a second recording layer (referred to as a “L1 layer” in this application, as occasion demands) as a second layer, which is located on the rear side of the semi-transparent reflective film via a middle layer, such as an adhesive layer. Moreover, it has a reflective film located on the rear side of the second recording layer. Then, in preparing such a multilayer type information recording medium, the L0 layer and the L1 layer are separately formed, and bonded to each other in the end, to thereby manufacture the dual-layer type optical disc at low cost.
Then, on the information recording apparatus, such as a CD recorder, for recording information onto the dual-layer type optical disc, the information is recorded into the L0 layer in an irreversible change recording method, performed by irreversible change recording heating by heating or the like, or in a rewritable method, by focusing (or irradiating) the laser light for recording on the L0 layer. Moreover, the information is recorded into the L1 layer in the irreversible change recording method performed by irreversible change recording heating by heating or the like, or in the rewritable method, by focusing the laser light on the L1 layer.
Patent document 1: Japanese Patent Application Laying Open NO. 2002-352469